Magnification viewers are well known in the art and generally comprise one or more optical loupes coupled to eyeglass frames. These magnification viewers are often worn by dentists and surgeons for extended periods of time during clinical procedures so as to provide clarity of view while avoiding a “hunched over” position that can result in debilitating neck and back strain, and which can, in turn, have an adverse effect on the success of the operation. By permitting the clinician to operate at a greater working distance from the patient, higher magnification viewers also reduce the clinician's exposure to potential contamination from aerosols.
Because clinicians use magnification viewers during surgery and other procedures requiring manual precision, it is important that they be light-weight, comfortable, and provide good clarity and a wide field of vision while providing high resolution.
The optical loupes of clinical magnification viewers are generally made according to the Galilean telescope design, having a single objective lens and a single eyepiece lens. Galilean telescopes are characterized by relatively narrow fields of view that are mainly limited by the diameter of the objective lens. The basic Galilean design, however, produces substantial chromatic aberration (“coloring”) and, hence, poor image quality.
Since the optical loupes should be kept as short as possible to reduce torque on the nose and general wearer discomfort, an eyepiece with a shorter focal length is usually employed when an increase in magnification is desired. However, to retain a good field of view without vignetting, the diameter of the objective must also be increased. If this is done while keeping the focal length of the objective the same, the “speed” of the lens increases, resulting in a lower resolution quality. It also mandates an excessively large package. One method of overcoming the “speed” problem is to use a more complicated objective lens, though at a cost of greatly increased weight and, therefore increased strain and discomfort to the wearer.
The so-called “Kellner design” (from Kellner, U.S. Pat. No. 1,197,742) in general use today contains a heavy doublet objective and a singlet eyepiece lens. While image quality is adequate at lower magnifications, excessive coloring results in poor image quality at higher magnifications. Moreover, the field of view is relatively limited in Kellner lens systems.
It is known that image quality of prior art magnification viewers can be enhanced by the use of “very high index flint glass.” However, this method has not been in general use, since “very high index flint glass” generally makes the viewer too heavy for practical use. Prior art magnification viewers also require lens mounting barrels of differing sizes in order to provide a wide range of focusing or working distances. As such, the manufacturing costs for these types of prior art viewers are relatively high.
There is thus a need for an improved magnification viewer capable of providing increased magnification while overcoming drawbacks of prior art viewers, such as those described above.